package com.itheima.algorithm.sort;

import java.util.Arrays;

// 归并排序
public class MergeSortTopDown {
    /*
       a1 原始数组
       i~iEnd 第一个有序范围
       j~jEnd 第二个有序范围
       a2 临时数组
    */
    public static void merge(int[] a1, int i, int iEnd, int j, int jEnd, int[] a2) {
        int k = i;
        while (i <= iEnd && j <= jEnd) {
            if (a1[i] < a1[j]) {
                a2[k] = a1[i];
                i++;
            } else {
                a2[k] = a1[j];
                j++;
            }
            k++;
        }
        if (i > iEnd) {
            System.arraycopy(a1, j, a2, k, jEnd - j + 1);
        }
        if (j > jEnd) {
            System.arraycopy(a1, i, a2, k, iEnd - i + 1);
        }
    }

    public static void sort(int [] a1){
        int[] a2 = new int[a1.length];
       split(a1,0, a1.length - 1, a2);
    }

    private static void split(int[] a1, int left, int right, int[] a2) {
        int[] array = Arrays.copyOfRange(a1, left, right + 1);
        System.out.println(Arrays.toString(array));
        // 2.治
        if (left == right) {
            return;
        }
        // 1.分
        int m = (left + right) >>> 1;
        split(a1 ,left , m, a2);
        split(a1, m+1, right, a2);
        // 3.合并
        merge(a1,left,m,m+1,right,a2);
        System.arraycopy(a2,left,a1,left,right-left+1);
    }
    public static void main(String[] args) {
        int []a = {9,3,7,2,8,5,1,4};
        System.out.println(Arrays.toString(a));
        sort(a);
        System.out.println(Arrays.toString(a));
    }
}
